[Recent findings on generators of evoked potentials]. / Recenti acquisizioni sui generatori dei potenziali evocati.

In the study of potential generators the dipole localization method is often used. The "equivalent dipole" represents the resultant of all the neurobiological processes (excitatory and inhibitory post-synaptic potentials, action potentials) that concur to generate the evoked potentials. According to the dipole's distance from the active electrode, "near-field" and "far-field" potentials will be recorded, with differences in the spatiotemporal distribution to the skin. The main hypotheses about the generators of standard components of somatosensory evoked potentials (SEP) from median and posterior tibial nerve, visual evoked potentials (VEP), auditory brainstem evoked potentials (BAEP) and P300, are analyzed.

A longitudinal study of multimodal evoked potentials in diabetes mellitus.

Abnormal findings in visual (VEP), brainstem auditory (BAEP) and somatosensory (SEP) evoked potentials at early stages of Type 1 and Type 2 diabetes have recently been reported by our group. Our aim here was to perform a longitudinal study in diabetic patients at an early stage of the disease using a combined evoked potential analysis in order to evaluate the variation of neurological abnormalities over time. Nine Type 1 and 12 Type 2 diabetic patients were examined and a second recording was carried out after a mean interval of 15.7 months +/- 6.2 SD. VEP, BAEP and SEP were measured in all patients. At the first recording electrophysiological abnormalities, present in both Type 1 and Type 2 diabetes were more evident when a multimodal evaluation was used (44.4% and 66.7% respectively). The follow-up study showed that overall neurological abnormalities persisted in all those patients who had previously presented pathological values. Whereas the number of patients with pathological values remained unmodified, a tendency to progression, namely the number of nervous levels with electrophysiological abnormalities, was observed. Thus, our study confirms the appearance of anatomofunctional disorders in the central nervous system in short-term diabetes, shows the persistence of neurological impairment in such patients and reveals a progressive segmental involvement at different nervous levels.

Multimodal evoked potentials in neuro-Behçet: a longitudinal study of two cases.

Two neuro-Behçet patients have been studied, over a period of several months, by means of peroneal and median somatosensory- (SEP), brainstem auditory- (BAEP), and visual- (VEP) evoked potentials. In both patients, peroneal SEP showed evidence of a pathological reduction in the central conduction velocity without a related deep sensation impairment, while VEP changes were consistent with the visual disorders. Conversely, BAEP and median SEP findings did not show disease-related abnormalities. The observed anomalies were detectable irrespective of the clinical phase of the disease. Thus, evoked potential assessment is useful in providing objective evidence for evaluating and monitoring CNS damage in neuro-Behçet's syndrome.

Brainstem auditory evoked potentials in toxic, metabolic and anoxic coma.

The aim of this study was to evaluate the efficacy of brainstem auditory evoked responses as a prognostic tool in conditions of coma which interfere with cerebral metabolism. Thirteen patients in coma resulting from different systemic disorders (barbiturate intoxication, cardiac arrest, chronic hepatic insufficiency) were included in the study. Brainstem auditory evoked potentials were recorded and patients were graded according to the results. When used in conjunction with other clinical parameters (Glasgow Coma Scale), brainstem auditory evoked potentials provided a more reliable prognostic tool than the traditional EEG exam alone. A good correlation was found between electrophysiological data and clinical outcome not only in barbiturate (toxic) coma, but also in hepatic (metabolic) coma. Of particular significance was the disappearance of the components which follow wave III (grade 2), leading to a fatal outcome in all three patients in hepatic coma.

Early detection of neurological involvement in IDDM and NIDDM. Multimodal evoked potentials versus metabolic control.

Clarification of the extent and mechanisms of damage to the central nervous system in diabetes is a frontier of current neurological research. Our aim was to obtain ample electrophysiological documentation of possible neurological abnormalities in both insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetic patients with a short duration of disease and without overt complications, taking into account metabolic control. Group 1 comprised 11 IDDM patients, and group 2 included 14 NIDDM patients treated with diet alone; the duration of disease was less than 4 yr, and no concomitant clinical complications were present. Age- and sex-matched normal subjects formed groups 3 and 4. Pattern visual evoked potentials (VEP), brain stem auditory evoked potentials (BAEP), and somatosensory evoked potentials (SEP; after the stimulation of both median and tibial nerves) were recorded in all subjects, and metabolic control was evaluated in terms of glycemia and glycosylated hemoglobin. In group 1, significant abnormalities were found in the latency values of VEP, median SEP, and tibial SEP compared with control subjects. Similar latency abnormalities were shown in group 2 for VEP, median SEP, and tibial SEP values and for wave I latency of BAEP. Glycosylated hemoglobin values were correlated with BAEP and SEP abnormalities in many patients in both groups. Furthermore, in group 2, glycemic values correlated with SEP abnormalities. We therefore conclude that neurophysiological abnormalities are present at different levels in IDDM and NIDDM patients only a few years after clinical diagnosis and before the appearance of overt complications, and these abnormalities seem to be correlated with metabolic control status.

Multimodal evoked potentials and CSF findings in the diagnosis of multiple sclerosis.

A group of 30 patients classified on clinical grounds as having definite (N = 16) or probable MS (N = 14) according to McAlpine's criteria, has been studied using multimodal recordings of evoked potentials (visual, auditory, and somatosensory) and examination of the cerebrospinal fluid (CSF) for oligoclonal bands and Link's Index. Evoked potentials examination proved extremely sensitive in discovering asymptomatic lesions of the central nervous system. CSF data, in particular the presence of oligoclonal bands, had a high sensitivity for MS. According to these electrophysiologic and immunologic results, we have reclassified our patients in conformity with the diagnostic criteria proposed by Bartel. The combination of electrophysiological and CSF data, together with common clinical criteria, led to greater diagnostic accuracy, making it possible to reclassify most patients previously considered to have probable MS as having definite MS.